Light-emitting diodes are power-saving and highly-efficient light sources, and can be applied to lighting, backlights in displays, and traffic indicators, etc. based on different wavelengths of emitted light. In addition to different requirements of wavelengths of emitted light, desired radiation patterns of the emitted light and enhanced brightness are also required according to different needs of each application.
In order to obtain desired radiation patterns, housing packages, lenses and reflectors are adopted to adjust radiation patterns. FIG. 12 shows a radiation pattern of a light-emitting diode chip 100. Referring to FIG. 13 to FIG. 14, to improve the vertical spread of the radiation pattern, a housing package 200 or a lens 300 can be used to package a light-emitting diode chip 100, so as to obtain a directional radiation pattern of the light-emitting diode chip. However, the volume of the packaged light-emitting diode chip is much larger than the volume of the original light-emitting diode chip.
Referring to FIG. 15, a conventional light-emitting diode chip 100 comprises a substrate 101, a Distributed Bragg Reflector structure 102 on one surface of the substrate 101, an active layer 103 on the Distributed Bragg Reflector structure, a capping layer 104 on the active layer, a first electrode 105 on the capping layer 104, and a second electrode 106 on another surface of the substrate 101 opposite to the Distributed Bragg Reflector structure 102. After injecting a current through the first electrode 105 and through the conventional light-emitting diode chip 100, the active layer 103 emits light. As shown in FIG. 12, an emission light 1031 substantially normal to the active layer 103 and towards the capping layer 104 escapes from the front of the conventional light-emitting diode chip 100, and an emission light 1032 substantially normal to the Distributed Bragg Reflector structure 102 and towards the substrate 101 escapes from the front of the conventional light-emitting diode chip 100 as well after being reflected by the Distributed Bragg Reflector structure 102 reflecting emission at specific wavelength. However, an emission light 1033 impinging on the Distributed Bragg Reflector structure 102 at an oblique angle of incidence escapes downwardly from the side of the conventional light-emitting diode chip 100 through refraction. As a result, the conventional light-emitting diode chip enhances only reflection of normal incidence instead of concentrating light escaping from the side of the conventional light-emitting diode chip to the front of the conventional light-emitting diode chip, and the efficiency thereof is not very good. Besides, a housing package or a lens is needed to adjust the radiation pattern.
Nevertheless, equipment and electronic devices nowadays follow the trend towards downsizing, and thus the conventional packaged light-emitting diodes are difficult to apply to the downsized equipment or electronic devices due to the enlarged volume after packaging.
The above light-emitting diode is able to combine with a submount to form a lighting device. The lighting device comprises a submount with a circuit; a solder on the submount, by which the above light-emitting diode can be fixed on the submount, and the substrate of the above light-emitting diode is electrically connected to the circuit on the submount; and an electrical connection structure for electrically connecting the pads of the light-emitting diode and the circuit on the submount; wherein the above submount could be a lead frame or a large mounting substrate for facilitating the design of the electrical circuit of the lighting device and increasing the heat dissipation efficiency.